TWI494705B - Projection exposure method, projection exposure system and projection objective - Google Patents

Description

Projection exposure method, projection exposure system and projection objective

The present invention relates to a projection exposure method for exposing a radiation-sensitive substrate disposed on an image surface area of a projection objective by using at least one image of a reticle pattern disposed on a surface area of an object of the projection objective. The invention further relates to a projection exposure system suitable for carrying out the method and to a projection objective suitable for use in such a projection exposure system.

Semiconductor components and other fine patterned components are currently fabricated using lithographic projection exposure methods and systems. The lithographic projection exposure procedure involves the use of a reticle (mask) carrying or forming a structural pattern to be imaged. The pattern is positioned between the illumination system of the projection exposure system and the projection objective, and is in the region of the surface of the object that projects the objective. The primary radiation source provides primary radiation and is converted by the optical components of the illumination system to produce illumination light that is directed to the reticle pattern in the illumination field. The radiation modified by the reticle and the pattern passes through the projection objective lens, and the projection objective lens is provided with an image in which the image surface of the substrate to be exposed is patterned. The substrate typically carries a radiation sensitive layer (resistance).

When a lithographic projection exposure system is used to fabricate an integrated circuit, the reticle (mask) may contain circuit patterns corresponding to individual layers of the integrated circuit. This pattern can be imaged onto an exposed area on a semiconductor wafer that is a substrate. The exposed area is sometimes referred to as a grain. A die in the background of an integrated circuit is a block of semiconductor material on which a predetermined functional circuit is to be fabricated. A single wafer typically contains a large number of adjacent grains, with the grains being successively exposed to the pattern image.

In one type of lithographic projection exposure system, illumination of each die is performed by exposing the entire reticle pattern to the die once. Such devices are commonly referred to as wafer steppers.

The alternate exposure system is referred to as a step-and-scan device or a wafer scanner, and each exposure region is effective by moving the reticle relative to the effective object field of the projection objective in the individual scanning directions, and simultaneously with respect to the conjugate of the projection objective. The projected beam of the image field moves the substrate and is gradually illuminated during the scanning operation. The reticle is typically held by a reticle holder that can be moved parallel to the surface of the object of the projection objective in the scanning device. The substrate is typically held by a substrate holder that is movable parallel to the image surface in the scanning device. The scanning directions may for example be parallel to each other or anti-parallel to each other. During the scanning operation, the moving speed of the reticle is related to the moving speed of the substrate and the magnification β of the projection objective, which is less than 1 in order to reduce the projection objective.

Forming a realistic pattern image with sufficient contrast on the substrate requires that the substrate surface be positioned in the focus area of the projection objective when exposed. More specifically, the surface of the substrate should be placed in the depth of focus (DOF) region of the projection objective, which is proportional to the Rayleigh unit, defined as RU = λ / NA ² , where λ is the operation of the projection exposure system Wavelength, and NA is the image side numerical aperture of the projection objective. For example, deep ultraviolet (DUV) lithography with λ = 193 nm typically requires a projection objective having a numerical aperture of 0.75 or higher to achieve a characteristic of 0.2 μm or less. In this NA region, the depth of focus is typically tens of microns. In general, as the resolution of the projection system increases, the depth of focus tends to decrease.

It has long been known that systems with a relatively narrow depth of focus may require specific techniques to ensure that the exposed areas on the substrate are in focus during exposure. For example, US 6,674,510 B1 discloses a method of producing a height map of a substrate at a measuring station. The height map is the physical reference surface of the substrate table used to secure the substrate during the reference exposure. At the exposure station, the height of the solid reference surface is measured and associated with the focal plane of the projection objective. The height map of the substrate is then used to determine the optimum height and/or tilt of the substrate table, while the exposed areas of the substrate are positioned at the best focus during exposure.

Another lithographic projection device is disclosed in WO 99/32940, in which a height measurement method is used.

The result of the gravity error causing the shape of the reticle to deviate from the planar shape can also introduce imaging errors. This effect is often referred to as "mask bending." The applicant's published international application WO 2006/013100 A2 discloses a projection objective that is specifically corrected for distortion effects caused by reticle bending.

It is an object of embodiments of the present invention to provide a progressive-scan projection exposure method that allows for high quality imaging to a substrate having an uneven substrate surface.

Another object of embodiments of the present invention is to provide a progressive-scan projection exposure method that allows for high quality imaging to be formed by the image to be imaged on the surface of the opaque mask.

In order to achieve the above and other objects of the present invention, in accordance with an embodiment of the present invention, a projection exposure method is provided, comprising: at least one image of a pattern of a reticle disposed on a surface of an object of a projection objective, in an scanning operation, an exposure setting In the exposure area of the radiation sensitive substrate on the image surface of the projection objective, the scanning operation is included in the individual scanning direction, moving the reticle relative to the effective object field of the projection objective, and moving the substrate relative to the effective image field of the projection objective; During the aiming operation, the imaging properties of the projection objective are actively changed according to a predetermined time profile to dynamically change at least one aberration between the beginning and the end of the scanning objective of the projection objective, wherein:

(i) the step of varying at least one aberration of the projection objective comprises: spatially resolving the optical effect caused by at least one field element of the projection objective, the field element comprising at least one optical surface disposed on the surface of the field optically adjacent to the projection objective Beam path

(ii) at least one field element is a mirror having a reflective surface disposed in a projected beam path optically close to the surface of the field;

(iii) the step of altering at least one imaging property of the projection objective comprises: changing the optical properties of the mirror by changing the surface profile of the reflective surface of the mirror in an optically used area.

The preferred embodiment is shown in the dependent claims. All terms used in the scope of the patent application are incorporated by reference.

The inventors have recognized that conventional methods of ensuring that fine structures are focused onto a substrate may not be sufficient for all conditions to ensure that a high yield of properly exposed substrate is obtained, thereby reducing the reject rate. In particular, it has been recognized that the reject rate may be significantly affected by local unevenness of the substrate surface in the exposed area. If the relative position of the substrate surface in the exposed area exceeds the acceptable range as the exposed area changes, the portion of the pattern to be imaged in the exposed area may not be sufficient for defining the structured component, thereby increasing the component during use of the component. The possibility of a failure.

For example, this potential problem can be simplified when considering the following: The depth of focus of a projection system typically designed to print 45 nm node images, typically having a depth of focus ranging from about 100 nm to about 150 nm. The specifications published by the International Technical Guidelines for Semiconductors (2006 update, Table 67a) indicate that the flatness SFQR of the wafer substrate in the exposed area of the scanner system 26 mm x 8 mm may correspond to direct random access memory (DRAM). The 1/2 pitch value of the associated DRAM. For example, when printing structures characterized by a 1/2 pitch of 45 nm of DRAM, those specifications allow for wafers having a site flatness of 45 nm in the exposed area of the scanner. The means to accurately place the surface of the substrate within the focus range of the projection objective may not be sufficient to cope with the value of the allowable roughness of the substrate surface in the exposed area of the future scanning system.

In a projection exposure method according to one aspect of embodiments of the present invention, active manipulation of the properties of the projection objective image is performed during a scanning operation, that is, during a time interval between the start of a single scan and the end of a single scan, wherein the substrate is relatively The effective image field of the projection objective is moved to continuously print a portion of the pattern of the reticle on the substrate. The active manipulation causes at least one aberration property of the projection objective to dynamically change in a targeted manner during the scan according to a predetermined schedule. This manipulation can be effected by actuating at least one manipulation device that operatively connects the optical elements of the projection objective to actively change the optical effect of the manipulated optical element, thereby actively changing the imaging properties of the entire projection objective.

Embodiments may be characterized by the fact that the field curvature of the projection objective dynamically changes during a scanning operation according to a predetermined schedule. Therefore, the imaging properties of the projection objective can be very efficiently matched to the time-dependent variation of the substrate surface position and/or the substrate surface shape in the exposure region. Alternatively or additionally, dynamic changes in the field curvature of the projection objective during scanning may also be used to match variations in surface shape and/or surface position on the object side of the projection objective. The reticle effect caused by, for example, the influence of gravity and/or the force or moment applied to the reticle can be at least partially compensated.

In systems where optical properties drift over time, for example, the optical properties of the focus position may change slowly (with a small time constant) in one direction, while the optical properties change little during a single scan operation, and only in one direction. In contrast, in the highly dynamic compensated embodiment, at least one aberration of the projection objective is continuously changed in two opposing directions between the beginning and the end of the scanning operation. In other words, the change in direction can be changed only once or more during a single scan operation. In doing so, it is possible to compensate for the negative effects of a dome or a valley-like shape having a typical size of the exposed area size.

In general, it may be difficult to vary one imaging aberration in a separate manner without affecting other imaging aberrations. Therefore, other aberrations, especially other field aberrations such as distortion, coma, out-of-focus field contours, astigmatism, and superposition, can change synchronously with changes in field curvature.

In some embodiments, the step of altering at least one imaging property of the projection objective comprises spatially altering an optical effect caused by at least one field element of the projection objective. The term "field element" as used herein relates to an optical element comprising at least one optical surface disposed on a surface of a projection beam that is optically adjacent to the surface of the projection objective. Actively changing the optical effects caused by the field elements allows for relatively large correction effects on field aberrations (such as field curvature and distortion) while allowing for wavefront aberrations such as astigmatism, coma, spherical aberration, And the effects of changes in higher-order aberrations remain small. Thus, the field element can be used to change the field aberration in a targeted manner while not substantially causing parasitic coma. There are many ways to characterize a position as "optical near-field surface." In general, it may be useful to utilize a paraxial sub-apetrre ratio SAR to define the axial position of an optical surface such as the surface of a lens or mirror, which is defined herein as follows:

SAR=(sign CRH) _* (MRH/(∣MRH∣+∣CRH∣))

In this definition, the parameter MRH represents the marginal ray height, and the parameter CRH represents the paraxial principal ray height of the imaging program. For the purposes of this case, the term "primary ray (also known as primary ray)" as used herein refers to light that travels from the outermost field point of the effective object field (the farthest from the optical axis) to the center of the entrance pupil. In a rotationally symmetric system, the chief ray may be selected from an equivalent field point in the meridional plane. In a projection objective that is substantially telecentric on the object side, the chief ray is emitted from an object surface that is parallel to the optical axis or has a very small angle with respect to the optical axis. The imaging program is further characterized by the trajectory of the edge rays. As used herein, "edge ray" is light that travels from an axial object field point (a field point on the optical axis) to the edge of the aperture stop. When using an off-axis effective object field, edge light may not contribute to image formation due to vignetting. Both the chief ray and the edge ray are used for the 傍 axis approximation. The radial distance between such selected rays and the optical axis at a predetermined axial position is expressed as "principal ray height" (CRH) and "edge ray height" (MRH), respectively. The ray height ratio RHR=CRH/MRH can be used to characterize the proximity or distance from the field surface or the 瞳 surface.

The definition of the edge light and the principal axis of the x-axis can be found, for example, in "Fundamental Optical Design" by Michael J. Kidger, SPIE PRESS, Bellingham, Washington, USA (Chapter 2), which is incorporated herein by reference. As a reference.

The biaxial subaperture ratio defined herein is an amount with a sign that provides a means of describing the relative proximity to the field plane or pupil plane, respectively, along the position of the optical path. In the above definition, the paraxial subaperture ratio is normalized to a value between -1 and 1, where the condition of SAR = 0 is for the field plane and SAR = -1 to SAR = +1 or A discontinuity point that jumps from SAR=+1 to SAR=-1 corresponds to the pupil plane. Thus, an optical surface positioned optically close to a field plane (e.g., an object surface or an image surface) is characterized in that the value of the pupil axis aperture ratio is close to zero, and the axial position of the optical proximity to the pupil surface is characterized by: the pupil axis aperture The absolute value of the ratio is close to 1. The sign of the 傍-axis sub-aperture ratio indicates that the position of the plane is optical upstream or downstream of the plane. For example, a sub-aperture ratio at a small distance downstream of the crucible surface and a small distance upstream of the crucible surface may have the same absolute value, but the opposite sign, because the chief ray height changes sign as it passes through the crucible surface.

In view of these definitions, a field element can be defined as an optical element having at least one optical surface disposed more optically closer to the field surface than near the surface of the crucible. The preferred location of the optical proximity to the field surface can be characterized by a light height ratio absolute value RHR = CRH / MRH > 1. In other words, the typical optical surface of the "optical near-field surface" is the position where the absolute value of the main ray height CRH exceeds the absolute value of the edge ray height MRH.

In other descriptions, the surface of the "optical near-field surface" may be characterized by a sub-aperture aperture ratio close to zero. For example, on the optical surface of the field element, the paraxial subaperture ratio SAR can be in the range between 0 and about 0.4 or between 0 and 0.2.

In some embodiments, the field element is placed in close proximity to the next field surface such that no optical elements are disposed between the field element and the closest field surface.

The field element can be an optical element of the projection objective. The field element may also be disposed between the object surface of the projection objective and the object side incident surface of the projection objective, or between the image side exit surface of the projection objective and the image surface.

The field element for aberration manipulation can be a transparent optical element in the projected beam path. In this case, the optical effect of the transparent optical element can be varied or changed in a spatially resolved manner (depending on the position within the area used by the optics) by varying the spatial distribution of the refractive power in the area used for optics. For this purpose, the two-dimensional distribution of the refractive index of the transparent optical element material can be changed in a targeted manner. This can be caused by, for example, targeted local heating of the transparent material. A potentially suitable structure is disclosed, for example, in WO 2008/034636 A2, the disclosure of which is incorporated herein by reference. Alternatively or additionally, the local distribution of refractive power can be varied by varying the spatial distribution of the local surface curvature of the optical surface of the transparent optical element. This can be caused by, for example, a target morphing optical element. An example of a manipulator is shown, for example, in US 2003/0234918 A1. A combination of changing the refractive index and changing the local distribution of surface curvature can be used. Furthermore, the manipulation can be carried out by a relative displacement of the aspherical surface having a complementary shape, as shown, for example, in EP 0 851 304 B1. An optoelectronic controller can also be used. The architecture and operation of the conventional manipulator may need to be modified to be sufficiently dynamic.

While the transparent optical field elements can be designed to have substantially refractive power in each configuration, the transparent optical field elements can also be shaped to be parallel to the plane of the board that is substantially free of overall optical capability. The field elements of such a picture plate can be placed very close to the field surface in many types of projection objectives, such as near the surface of the object, or in a projection objective that forms at least one actual intermediate image, near the intermediate image.

In some embodiments, at least one field element is a mirror having a reflective surface disposed in a projected beam path optically near the field surface. Varying the optical properties of the mirror can include changing the surface profile of the reflective surface in the area used for optics. The mirror manipulators are each operatively coupled to the field lens and are configurable to allow the shape of the reflecting surface of the field lens to be changed in one or two dimensions.

The number of degrees of freedom to dynamically change the imaging properties of the projection objective can be increased by providing at least two field elements that can be manipulated independently of each other in a predetermined coordinate manner. For example, the projection objective can include two reflective field elements (field mirrors), each optically close to the field surface. Each field mirror can be assigned a mirror manipulator to change the shape of the reflecting surface of the field mirror in a targeted manner.

The applicant's U.S. Patent No. 7,385,756 discloses a projection objective on a catenary having two intermediate images and two concave mirrors, each concave mirror being disposed near the center, i.e., relatively close to the field surface. Both concave mirrors can be used as a manipulator. The disclosure of this document is incorporated herein by reference.

At least one field element can be placed close to the surface of the object. In some embodiments, the transparent field element forms a first element of the projection objective immediately after the surface of the object, and the incident surface of the field element forms the incident surface of the projection objective. Therefore, a strong influence on the field aberration can be obtained without substantially affecting the coma aberration to a significant extent. In a projection objective that produces at least one actual intermediate image between the surface of the object and the intermediate image surface, the field element can be placed optically close to the intermediate image. In some embodiments, the projection objective has at least two or exactly two intermediate images. The field elements can be arranged to be optically adjacent to each intermediate image surface, which is the field surface of the projection objective.

Regarding the dynamics of typical manipulations, it is contemplated that modern scanning systems can operate at scan speeds, for example, from about 0.2 m/s to about 2 m/s. Scan speeds range from 700 mm/s to 800 mm/s. Typical scan path lengths can be on the order of 10 mm (eg 30 mm-40 mm). This allows each exposure zone (die) to have an exposure time of the order of 10 ms (microseconds). Considering the typical value of about 50ms scan time per die, the dynamics of the control can be on the order of 20 Hz or more, in typical cases for example 40 Hz or more, or 60 Hz or more, or 80 Hz or more. , or 100 Hz or more, or 120 Hz or more.

Regarding the magnitude of the maneuver, considering the local curvature peak-valley local variation at ±45 nm is sufficient to achieve a reasonable degree of compensation in many high NA systems. Such high NA systems may have a maximum available NA at a level of NA = 0.8 or higher, such as NA 0.9, or NA 1, or NA 1.2, or NA 1.35.

Relatively speaking, it is currently considered that the rate of change of depth of focus (DOF) in the 10 ms (microsecond) is 10%, which in many cases is sufficient to achieve sufficient compensation. In some embodiments, the field curvature is varied by a rate of change of about 0.5% and about 50% of the focal depth of the projection objective over a 1 ms time interval.

In a negative effect embodiment for effectively compensating for substrate unevenness, the method may further comprise the steps of: generating substrate surface data representing a surface contour of the substrate in the exposed area; generating a manipulator control signal based on the substrate surface data; The control signal drives at least one manipulation device of the projection objective to dynamically adaptively project the imaging properties of the objective lens to reduce aberrations caused by the surface profile of the exposed area.

The surface material of the substrate can be produced by measuring the surface topography of the substrate in the measurement area including the exposed area. Alternatively, the substrate surface data can be derived from data contained in a lookup table that represents the surface topography of the substrate in the measurement zone containing the exposure zone. The data of the lookup table can be pre-experimented or calculated from the beginning. For example, the correction of the field curvature can be performed based on previous measurements of the surface topography of the substrate, and the compensation concept can be based on the data contained in the lookup table.

Therefore, aberrations caused by, for example, unevenness of the wafer surface can be compensated in a very efficient manner. The measurement can be performed by a conventional method. Possible reasons for wafer unevenness are, for example, substrate transfer procedures, as described in the following documents: HW van Zeijl, J. Su, J. Slabbekoorn, FGC Bijnen, "Lithographic Alignment for substrate transfer procedures" Offset Compensation for Substrate Transfer Process)", Proc. STW/SAFE, Veldhoven, The Netherlands, 2005, pp 121-126.

In an embodiment for effectively compensating for the negative effects of the reticle (eg, due to reticle bending), the method may further comprise the step of producing a reticle that represents a surface contour of the reticle in the reticle region of the corresponding exposure zone. Surface data; generating a manipulator control signal based on the reticle surface data; driving at least one manipulation device of the projection objective in response to the manipulator control signal to dynamically adaptively project the imaging properties of the objective lens to reduce the surface profile caused by the reticle region Aberration.

The reticle surface data can be generated by measuring the reticle surface topography in the measurement zone containing the reticle region of the corresponding exposure zone. Alternatively, the reticle surface data can be derived from data contained in a lookup table that represents the surface topography of the reticle in the measurement zone containing the reticle region of the corresponding exposure zone. The data of the lookup table can be pre-experimented or calculated from the beginning.

Therefore, aberrations caused by, for example, unevenness of the surface of the reticle can be compensated in a very efficient manner.

The foregoing and other features are not limited to the scope of the patent application, but also in the detailed description and drawings, wherein the individual features may be used in the embodiments of the present invention and other fields, alone or in combination, and may individually represent advantages and patents. Example.

In the following description of the preferred embodiment, the term "optical axis" means a straight line or series of straight segments passing through the center of curvature of the optical element. The optical axis can be folded by a folding mirror (biasing mirror) such that the continuous linear segments of the optical axis are angled. In the example shown below, the object is a reticle (mask) carrying an integrated circuit layer pattern or other pattern, such as a grid pattern. The pattern of the object is projected onto a wafer coated with a photoresist layer as a substrate, although other types of substrates may be used, such as components of a liquid crystal display or a grating substrate.

A list is provided to reveal the specifications of the designs shown in the drawings, and the tables or the tables have the same reference numerals as the respective drawings. Corresponding features in the figures have similar or identical reference numerals to facilitate understanding. When the lens is marked, the symbol L3-2 represents the second lens of the third objective portion (as viewed by the direction of radiation propagation).

1 schematically shows a lithographic projection exposure system in the form of a wafer scanner WS that utilizes immersion lithography in a step and scan mode to fabricate a large scale integrated semiconductor component. This projection exposure system contains an excimer laser having an operating wavelength of 193 nm as a primary radiation source S. Other primary sources of radiation may be used in other embodiments, such as emitting about 248 nm, 157 nm, or 126 nm. Radiation sources in the extreme ultraviolet (EUV) spectral range can also be used with purely reflective (reflective) optical systems. The illumination system ILL downstream of the source of light produces a large, clearly defined and homogeneously illuminated illumination field IF at its exit surface ES for matching the telecentric requirements of the downstream projection objective PO. The illumination system ILL has means for selecting an illumination mode, and in this example can be on-axis illumination with off-axis illumination with a variable degree of continuity (especially with an annular illumination zone in the pupil surface of the illumination system) Between ring illumination and bipolar or quadrupole illumination).

Disposed downstream of the illumination system is a device RS for supporting and manipulating the reticle M, such that the pattern formed on the reticle is positioned at the exit surface ES of the illumination system, which coincides with the object surface OS of the projection objective PO. The device RS for supporting and manipulating the reticle is commonly referred to as a "mask station" and includes a reticle holder and a scanner driver, wherein the scanner driver enables the reticle to be parallel to the projection objective during the scanning operation The object surface OS moves or is perpendicular to the optical axis of the projection objective and the illumination system moves in the scanning direction.

The reduced projection objective lens PO is designed to image the image of the pattern provided by the reticle onto the photoresist-coated wafer W (magnification|β|=0.25) at a reduced scale of 4:1. It can also be other reduction scales, such as 5:1 or 8:1. The wafer W used as the photosensitive substrate is disposed such that the macroscopic flat substrate surface SS having the photoresist layer substantially conforms to the flat image surface IS of the projection objective. The wafer is supported by a device WST (wafer table) that includes a scanner driver to move the wafer in parallel with the mask M in parallel with the mask. The wafer stage includes a z-manipulator for raising or lowering the substrate parallel to the optical axis, and a tilt manipulator device for tilting the substrate about two axes of the vertical optical axis.

The device WST (wafer table) for supporting the wafer W is constructed for immersion lithography. It contains a receiving device RD that can be moved by the scanner driver and has a flat recess at its bottom for receiving the wafer W. The peripheral edge forms an upwardly open and liquid-tight receiving portion for the liquid infiltration medium IM, and the liquid infiltration medium IM can be introduced into the receiving portion or discharged from the receiving portion by means not shown. The height of the edge is dimensioned so that the filled immersion medium can completely cover the surface SS of the wafer W, and the exit side end region of the projection objective lens PO can be immersed in the immersion liquid, and the objective lens exit and the wafer surface can be correctly set. The distance between operations.

The projection objective lens PO has a plano-convex lens PCL as the last optical element closest to the image surface IS, and the flat exit surface of this lens is the last optical surface of the projection objective lens PO. During operation of the projection exposure system, the exit surface of the final optical element is completely wetted in the wetting liquid IM and wetted by the wetting liquid IM.

In other embodiments, the exit surface is disposed at a working distance of a few microns above the substrate surface SS of the wafer such that there is a gas filled gap (dry system) between the exit surface of the projection objective and the substrate surface.

As shown in the schematic illustration of Figure 1, the illumination system ILL can produce an illumination field having a rectangular shape. The size and shape of the illumination field determines the size and shape of the effective object field OF of the projection objective that is actually used to project the reticle image of the image surface of the projection objective. The effective object field has a length A* parallel to the scanning direction and a width B*>A* in the cross-scanning direction in the vertical scanning direction, and does not include an optical axis (off-axis field).

Projection objective PO may comprise a plurality of schematically displayed lenses (typically having a number of lenses greater than 10 or greater than 15 lenses) and, if desired, other transparent optical components. The projection objective can be purely refractive (lens only). In addition to the lens, the projection objective may also comprise at least one power supply mirror, such as at least one concave mirror (refractive projection projection objective).

In the field of many lithography, the image side numerical aperture of the projection objective is NA > 0.6, and in many embodiments, NA is between about NA = 0.65 and NA = 0.95, which can be achieved by a dry objective. Using an immersion system allows for NA values of NA 1, for example NA 1.1, or NA 1.2, or NA 1.3, or NA 1.4, or NA 1.5, or NA 1.6, or NA 1.7, or above. Basically, depending on the combination of the image side NA and the wavelength of the radiation source, the typical resolution can also be as low as about 150 nm, or 130 nm, or 100 nm, or 90 nm, or lower.

The projection objective lens PO is an optical imaging system designed to form an image of an object disposed on the surface OS of the object in an image surface optically conjugate with the surface of the object. This imaging is obtained without the need to form an intermediate image or via one or more intermediate images (eg, two intermediate images).

Each optical system is associated with a basic field curvature, known as Petzval curvature, as explained in more detail below with reference to Figure 2A. When there is no astigmatism, the sagittal and tangential image surfaces match each other and are on the Petzval surface. A positive lens (a lens having a positive refractive power) introduces an inward bending of the Petzval surface into the system, and a negative lens (a lens having a negative refractive power) is introduced to be bent backward. Petzval curvature 1 / R _P is Petzval radius reciprocal for R _P corresponds (which is a Petzval sum of the radius of curvature of the surface) of the Petzval sum 1 / R _P given.

For example, the condition of R _P <0 is for a positive lens, corresponding to the inward bending of the Petzval surface. Thus, the image of the planar object will be concave toward the direction of radiation, where conditions are typically referred to as "undercorrection" of the field curvature. In contrast, the condition of R _P >0 is for a concave mirror, corresponding to excessive correction of field curvature. A flat image of the flat object can be obtained by an imaging system with R _P =0. These conditions for the projection objective are shown schematically in Figure 2A.

The Petzval surface and the 影像-axis image surface intersect at the optical axis. The curvature of the Petzval surface may cause the Petzval surface to move away from the ideal image surface for points away from the optical axis. The fact that the Petzval surface is curved translates into a field point at the outer edge of the image field (at the maximum image field height y'), and the Petzval surface exits p from the ideal image surface (usually flat) longitudinally, parallel to the image. The optical axis in the surface is measured. The term "image field curvature" is used to mean such a longitudinal departure (or sag) at the maximum image field height y' and "the curvature of the image field" that may not reciprocal to the radius of curvature of the image field. Confused.

Note that Figure 2 is purely schematic and does not scale to any of the features discussed in the figures.

The condition on the image side of the objective lens is explained in conjunction with FIG. 2B. For the purposes of this case, the size of the image field may be characterized by a maximum image field height y' corresponding to the radius of the (circular) "designed image field" of the objective lens. The design image field IF _D contains all the field points on the image surface, and the imaging medium accuracy of the objective lens is good enough for the desired lithography procedure. In other words, in an area having a radial coordinate equal to or smaller than the maximum image field height y', all aberrations are sufficiently corrected for the desired application, and one or more points outside the design image field IF _D Many aberrations may be higher than the required threshold.

In general, not all field points within the design image field IF _D are used for the lithography process. Rather, exposure is performed using only field points located within the effective image field IF, which should be large enough to permit exposure of a properly sized substrate in the lithography process. The effective image field must conform to the design image field IFD to include only field points sufficient to correct the objective and no vignetting. There are various ways to match the effective image field to the design image field depending on the design of the objective lens.

In the projection exposure system designed for scanning operations, a slit-shaped effective image field IF is used. 2B shows an example of a rectangular effective off-axis image field IF that can be used with the unshielded deflecting projection objective discussed below. In the soothing embodiment, an effective image field (sometimes referred to as a ring or ring field) having an arc shape can be used. The size of the effective image field is generally described by a length A parallel to the scanning direction and a width B > A perpendicular to the scanning direction, thereby defining an appearance ratio AR = B / A > 1. In many embodiments, the aspect ratio can range, for example, from 2:1 to 10:1.

The advanced scanning projection exposure system can be equipped with a wafer table that can move the substrate table parallel to the optical axis (z-manipulation) and can also tilt the wafer table around two mutually perpendicular axes perpendicular to the optical axis (x tilt and y tilt) ). The system is operable to offset or tilt the substrate table between exposure steps and to adjust the position of the substrate surface relative to the focus area of the projection objective based on the previously measured substrate surface (see, for example, US 6,674,510 B1).

However, those systems do not fully address the local unevenness of the substrate surface in the exposed area. Rather, a compromise position relative to the surface of the substrate of the focal region of the projection objective is typically obtained. however. The inventors have recognized that an uneven surface profile of the substrate in the exposed area may cause deterioration in the quality of the imaging process, thereby causing an increase in the reject rate of, for example, manufacturing of the microstructured semiconductor device.

Figure 3 shows schematically the principle of a wafer table (z-manipulation) that can be used to raise or lower the surface of a substrate parallel to the optical axis. In FIG. 3A, when z=0, the uneven substrate surface SS is entirely outside the focus position of the projection objective. Therefore, as shown in FIG. 3B, the focus position FOC is located above the substrate surface of the wafer W. If the wafer stage is raised in the axial direction by a predetermined amount (z-MAN), the uneven substrate surface may be in the best focus area, and at least a portion of the exposure area is focused, and the out-of-focus aberration (3C) is reduced. However, depending on the depth of focus, it may happen that the partially exposed areas are still out of focus above an acceptable threshold and thus may significantly deteriorate the contrast in at least a portion of the exposed areas.

In the following, the unevenness of the surface of the substrate can be regarded as interference of the lithography imaging program. For illustrative purposes, FIG. 4A shows an axial view of a semiconductor wafer W having a plurality of rectangular exposure regions ES (or grains) divided into two large-area rectangular exposure regions ES (or grains), wherein the exposure regions are disposed in adjacent grain networks, one at a time. Continuous illumination through the reticle. Each of the exposure regions has a width EAX corresponding to the width of the effective image field of the projection objective in the cross-scan direction (x-direction) and the length EAY, which may be equal to, greater than, or less than the width EAX, and substantially greater than the height A of the effective image field. 4B shows a vertical cross section (x-z cross section) of the substrate showing a multi-curved substrate surface SS. It is contemplated that after extensive adjustment of the axial position and the tilt angle of the entire substrate, local unevenness of the substrate surface results in a surface profile that has a substantially parabolic (quadratic) field profile in the x-direction, at least in the first approximation. The amount of deviation from the planar reference surface can be quantified by the peak-to-valley pv in the individual regions, which are defined herein as the difference between the minimum and maximum profile heights in the exposed regions. Further, since the high aspect ratio (for example, 4 < AR < 6) of the slit-shaped effective image field is considered, the bending of the substrate surface SS in the orthogonal y direction (scanning direction) can be ignored. Therefore, due to the high image side numerical aperture of the projection objective, the uneven surface profile of the substrate will cause at least the quadratic field profile of the out-of-focus in the first approximation and the quadratic field profile of the spherical aberration at the same time. Note that these aberrations are independent of the optical design of the projection objective and are only relevant to the image side NA of the projection objective.

In the following, wavefront aberrations caused by the projection system and/or caused by external conditions are represented as linear combinations of polynomials. In the field of optics, many types of polynomials are suitable for describing aberrations, such as the Seidel polynomial or the Zernike polynomial. The Nickel polynomial is used below to characterize the aberrations.

The technique of using the Nickel term to describe the wavefront aberration from the optical surface deviating from the perfect sphere is an advanced technique. It is also good to establish different disparity phenomena, including defocus, astigmatism, coma, and spherical aberration to higher aberrations. The aberration can be expressed as a linear combination of the selected number of Rennick polynomials. The Nickel polynomial is a set of fully orthogonal polynomials defined on a unit circle. For example, polar coordinates are used, where ρ is the normalized radius and θ is the azimuth. The wavefront aberration W(ρ, θ) can be developed by the Nickel polynomial to the sum of the product of the nick and the individual weighting factors (see, for example, the Optical System Handbook, Volume 2, Physical Image Formation (Handbook of Optical Systems: Vol. 2). , Physical Image Formation), edited by H Gross, Wiley-VCH Verlag GmbH & Co. KGaA, Chapter 20.2, (2005)). In the Renn representation, the Nickel polynomials Z1, Z2, Z3, etc. have some meaning to identify contributions to the overall aberration. For example, Z1=1 corresponds to a constant term (or a piston term), Z2=ρ cosθ corresponds to a distortion in the x direction (or a wavefront tilt in the x direction), and Z3=ρ sinθ corresponds to Distortion in the y direction (o or wavefront tilt in the y direction), Z4 = 2ρ ² -1 corresponds to out of focus (parabolic portion), Z5 = ρ ² cos2θ corresponds to third order of astigmatism and the like.

Any Nick polynomial can also be used to characterize the deviation of an optical surface, such as a lens surface or mirror surface, from a nominal surface, such as a spherical surface.

Figure 5 shows the Renak spectrum showing the effect of a substantially quadratic surface profile in the x-direction in the exposed region for substrate surface irregularities characterized by peak-to-valley PV = 100 nm in the exposed region. It is obvious that the unevenness basically affects the out-of-focus (Renix coefficient Z4) and spherical aberration (main spherical aberration Z9, minor spherical aberration Z16, etc.), while other images caused by uneven (non-planar) surface contours The level of difference is relatively small.

The following examples show how the imaging aberration caused by the uneven substrate surface in the exposure area of the scanning lithography apparatus can be significantly reduced. Figure 6A schematically shows a rectangular exposure area EA on the surface of an uneven wafer between two different instant times. At the first instant time t ₁ , the illuminated slit-shaped effective image field IF of the projection objective is positioned close to the lower edge of the exposure zone. As the scan progresses, the wafer moves in the scanning direction (y direction) relative to the fixed projection objective, such that the instant time t ₂ of the illuminated effective image field is at a different location from the first location. Typical values for scanning speed (eg between about 0.2 m/s and 2 m/s) and exposure zone sizes have a typical edge length of one or more centimeters, for example between 20 mm and 40 mm. The time interval Δt required for the entire exposed area to be illuminated by the illuminated image field in one scanning operation may typically be in the range of, for example, between about 10 ms and 200 ms.

Figure 6B shows individual segments of the substrate in the xz plane perpendicular to the scan direction. In one case, the image side end of the projection objective lens PO is displayed, and the exit side of the projection objective lens is separated from the uneven surface SS of the substrate by a working distance. The surface of the substrate has a convex surface shape at t ₁ , and the surface of the substrate is concavely curved at a later time t ₂ &gt _; t _{1 to} a spaced region traversed by the projection beam.

The dashed lines in each case represent the Petzval surface PS of the projection objective, which is adapted to conform to the surface topography of the substrate within the effective image field to allow for reduction of imaging aberrations caused by the surface of the uneven substrate. In the example, the field curvature with respect to the time t _1, the projection objective slight under-corrected, and the correction is dynamically changed to a state slightly excessively correcting time t _2. Significant changes in the curvature of the image field of the imaging system are dynamically implemented within the second fraction of the scan speed. This change is based on surface topography measurements performed prior to the scanning operation, as detailed below.

Considering that the scan time per die is typically about 50 ms, dynamic operation can be at a level of, for example, 20 Hz or more.

Relatively speaking, considering the rate of change in the 10% level of depth of focus (DOF) within 10ms (microseconds), it is sufficient for many cases to achieve sufficient compensation. In some embodiments, the out-of-focus is varied in a time interval of 1 ms with a rate of change of about 0.5% to about 50% of the depth of focus (DOF) of the projection objective.

The rate of change in imaging aberrations caused by the active manipulation of one or more optical elements of the projection objective, such as field curvature and/or distortion, may vary from ambient to environmental (eg, ambient pressure and/or temperature) when using the projection system. The change caused by the change) and/or the heating system causes the time dependent change to be on the order of several orders of magnitude faster.

The target manipulation effect of the projection object at one or more optical elements (field elements) that are relatively close to the surface of the individual field is now more detailed with the working example of a catadioptric projection objective suitable for immersion lithography of NA > 1. Individual exposure systems can be equipped with advanced manipulators to move the reticle and/or mask parallel to the optical axis, and to tilt the reticle and/or wafer about one or more tilt axes of the vertical optical axis. In addition, the exposure system can be equipped with a wavelength manipulator to shift the center wavelength λ of the system within the control range Δλ in the chromaticity correction state of the individual projection objective.

In each case, one or more additional manipulators may be specifically provided to address the effects of substrate surface irregularities and/or reticle irregularities, as explained in more detail below.

Figure 7 shows two axial sections of the catadioptric projection objective 700 of the first embodiment. In terms of the reduced imaging scale of 4:1 (β=-0.25), the projection objective is telecentric on the object side, and the image side numerical aperture NA=1.35 on the image side. The effective image field size is 26 mm x 5.5 mm. This specification is shown in Tables 7 and 7A. Figure 7A shows the segments in the x-z plane, while Figure 7B shows the segments in the y-z plane perpendicular thereto. The specifications for the system are derived from the embodiment shown in Figure 3 of US 2008/0174858 A1. This corresponding disclosure is hereby incorporated by reference.

The projection objective 700 is designed to project a pattern image placed on the reticle of the flat object surface OS (object plane) onto a flat image surface IS (image plane) at a reduced scale, for example 4:1, wherein exactly two actual images are produced. Intermediate images IMI1, IMI2. The rectangular effective object field OF and the image field IF are off-axis, that is, the whole is outside the optical axis OA. The first refractive objective portion OP1 is designed to image the pattern of the surface of the object as the first intermediate image IMI1. The second reflection (pure reflection) objective lens portion OP2 images the first intermediate image IMI1 as a second intermediate image IMI2 at a magnification close to 1: (-1). The third refractive objective portion OP3 images the second intermediate image IMI2 to the image surface IS with a strong reduction ratio.

The projection objective 700 is an example of a "chain" projection objective having a plurality of series of objective portions, each serving as an imaging system, and an image generated by a previous imaging system on the radiation path via an intermediate image link (intermediate image) As an object of the subsequent imaging system on the radiation path. The subsequent imaging system can produce another intermediate image (e.g., second objective portion OP2) or the last imaging system that forms the projection objective, which produces a "final" image field (similar to the third objective portion OP3) on the image plane of the projection objective.

The principal ray CR path of the outer field point of the off-axis object field OF is shown in Figure 7B to help follow the beam path of the projected beam.

Three mutually conjugated tantalum surfaces P1, P2, and P3 are formed at positions where the chief ray intersects the optical axis. The first pupil surface P1 is formed on the first objective portion between the surface of the object and the first intermediate image, and the second pupil surface P2 is formed on the second objective portion between the first intermediate image and the second intermediate image, and the third aperture The surface P3 is formed in a third objective portion between the second intermediate image and the image surface.

The second objective lens portion OP2 includes a first concave mirror CM1 having a concave mirror surface facing the object side, and a second concave mirror CM2 having a concave mirror surface facing the image side. The portion of the mirror surface used, i.e., the mirror surface area that is illuminated during operation, is continuous or unbroken, i.e., the mirrors do not have holes or holes in the illuminated area. The mirror surfaces facing each other define a catadioptric cavity surrounded by a curved surface defined by a concave mirror, which is also referred to as an endoscopic space. The intermediate images IMI1 and IMI 2 are both inside the folding reflection chamber and away from the mirror surface.

The objective lens 700 is rotationally symmetric and has a straight optical axis ("online system") common to all of the refractive and reflective optical components. There are no folding mirrors. An even number of reflections occur. The optical surface and the image surface are parallel. The concave mirrors have a small diameter and are allowed to be placed close together and fairly close to the intermediate image positioned therebetween. The concave mirrors are both constructed and deflected into an off-axis section of the axially symmetrical surface. The beam passes through the edge of the concave mirror facing the optical axis without vignetting. The concave mirrors are all optically positioned away from the surface of the crucible quite close to the next intermediate image. The objective lens has an unobscured circular ridge that concentrates around the optical axis, thus allowing the use of a projection objective as a lithography.

The concave mirrors CM1, CM2 are all disposed optically close to the field surface formed by the next intermediate image, as shown in Table A below, providing information on the edge ray height MRH, the chief ray height CRH, the ray height ratio RHR, and the subaperture ratio SAR. :

The position of the optical near the surface of the field can also be characterized by the shape of the projected beam at the individual surface. At the optical surface optically near the surface of the field, the cross-sectional shape of the projected beam deviates significantly from the circular shape typically found at or near the surface of the crucible. As used herein, the term "projected beam" describes all beams of light that travel from the effective object field on the surface of the object toward the effective image field of the image surface. The position of the surface of the optical near-field surface can be defined as the position at which the beam diameters of the projected beams can deviate from each other by more than 50% or more than 100% in two mutually perpendicular directions orthogonal to the direction of propagation of the beam. Typically, the illuminated area on the surface of the pupil near the surface of the field will have a shape that strongly deviates from the rounded end, similar to a high aspect ratio rectangle, corresponding to the preferred field shape in the scanning lithographic projection apparatus. As can be seen from Figure 9 below, the illuminated areas on the first concave mirror and the second concave mirror are substantially rectangular having rounded edges having an apparent ratio AR of the active object and the image field. The rectangle of the effective object field OF can be known by comparison between FIG. 7A and FIG. 7B, in which the object field is cut along the long side (x direction), and in FIG. 7B, the object field is parallel to the scanning direction. Cut, that is, parallel to the short side of the rectangular effective object field.

The primary function of the two concave mirrors CM1 and CM2 is to correct the Petzval sum by providing Petzval and excessive correction contributions to counteract the undercorrecting effects of the positive refractive power of the lens. The contribution of the concave mirror to the field curvature can be dynamically varied by changing the surface curvature of the reflecting surface according to a predetermined space and schedule. For this purpose, the first concave mirror and the second concave mirror are each associated with the mirror manipulators MM1, MM2, respectively, which are configured for the two-dimensional deformation (space-resolved deformation in two dimensions) for the relevant concave mirror during the scanning operation. The mirror manipulators can be identical or different in construction.

In the example, the concave mirrors each have a highly reflective (HR) coating on the elastic portion of the mirror surface. Some actuators (represented by arrows) of the mirror manipulator MM1 or MM2 are operatively coupled to the back side of the resilient portion. The actuator is controlled by a mirror control unit MCU, which can be an integral part of the central control unit of the projection exposure apparatus. A manipulator control unit is coupled to receive a signal indicative of the desired deformation of the mirror surface. The mirror manipulator and the corresponding control unit can be substantially designed, for example, as disclosed in the applicant's patent application No. US 2002/0048096 A1 or US 2005 0280910 A1 (corresponding to WO 03/98350 A2). Corresponding disclosures are hereby incorporated by reference.

However, any suitable architecture of the frog mirror manipulator can be used, such as a manipulator using an electromechanical actuator, such as a piezoelectric element, an actuator that responds to changes in fluid pressure, an electrical and/or magnetic actuator. These actuators can be used to deform a continuous (unbroken) mirror surface as described above. The mirror manipulator may also include one or more heating elements and/or cooling elements that effect local temperature changes to the mirror resulting in the desired mirror surface distortion. A resistive heater or Peltier element can be used for this purpose.

A two-dimensional deformation of both the first concave mirror CM1 and the second concave mirror CM2 during the scanning operation can be simulated for a wafer substrate having an uneven substrate surface, wherein the wafer substrate has a concave parabolic contour in the cross-scan direction (x direction) and is maximum The difference between the height minimum height is 45 nm (peak-valley of 45 nm) as shown in Fig. 4B. Three correction scenarios SC1, SC2, and SC3 were simulated.

In the first scenario SC1, the substrate irregularity is corrected in a conventional manner by actively manipulating the z-position of the wafer and the tilt state of the wafer, substantially as illustrated in FIG. In the second context SC2, an active manipulation of the plurality of optical elements is performed additionally, including relative displacement parallel to the optical axis and tilting the lens.

In the third scenario SC3, during the scanning operation, the surface shapes of both the first concave mirror CM1 and the second concave mirror CM2 are two-dimensionally deformed in a time-dependent manner to reduce aberration caused by unevenness of the substrate surface. Figure 8 shows a comparison of aberrations caused by quadratic irregularities (PV = 45 nm) in the three contexts SC1, SC2, and SC3. The overall induced aberration is decomposed into contributions as described by the Rennick coefficient, which is shown in the abscissa value of FIG. The ordinate shows the scanning aberration SCA in nm. In the case where the two mirrors of each optical near-field surface (intermediate image) are dynamically deformed during the scanning operation to improve the aberration, it can be seen that the scanning aberration is significantly improved. Both the out-of-focus aberration (Z4) and the wavefront tilt aberration (Z2/3) can be significantly reduced with respect to the standard situation SC2, and are more reduced with respect to the first situation SC1, which is only relative to the axial position and tilt Use optimized wafer locations. Both out-of-focus (Z4) and wavefront tilt (Z2/3) are about 90% lower than the standard scenario SC2, and even better than the pure wafer scenario SC1 by about 95%. For example, by dynamically deforming two concave mirrors, the out-of-focus aberration Z4 can be reduced from about 12 nm to about 0.6 nm. Similarly, a significant improvement can be obtained for astigmatism (Z5/6), which can be reduced by about 90% relative to standard context SC2.

These values indicate that the dynamic deformation of the field elements significantly reduces the contribution of substrate surface irregularities to the focus budget, which is one of the current leading contributions. This results in a significant improvement in program latitude in the lithography program. At the same time, the requirements for focus errors can be relaxed on other contributing effects, such as lens heating or the like.

Fig. 9 schematically shows the corrected deformation (Fig. 9A) applied to the first concave mirror CM1 and the corrected deformation of the second concave mirror CM2 (Fig. 9B) in order to obtain the desired improvement. In each case, the peak-to-valley (PV) deformation of the reflective surface is quite small and can range, for example, below 200 nm. In a particular case, the PV of CM1 is deformed by about 80 nm, while the PV of CM2 is deformed by about 160 nm. Further, the drawing schematically shows that the deformation of the relatively long wave is performed to reduce the aberration caused by the quadratic deformation of the long wave in the cross-scanning direction of the substrate surface. This means that in many cases the concave basic contour deviation of the mirror does not need to be very complicated, and the architecture of the individual mirror manipulator is quite simple. In general, multiple Ninescope manipulators can be used in each case, while allowing the reflective surface to be deformed in a targeted manner, which can be broken down to a high value of the Rennick coefficient, such as between Z2 and Z49. However, in many cases the deformation of less complex structures may be sufficient, allowing for the use of less complex mirror manipulators.

The compensation mechanism can be implemented in a projection exposure apparatus comprising a projection objective, wherein the projection objective has one or more manipulators associated with one or more optical elements of the projection objective by integrating the manipulator into the control system. For actively changing the imaging properties of the projection objective according to a predetermined table during a scanning operation, dynamically changing at least one aberration of the projection objective between the beginning and the end of the scanning operation. A manipulator associated with the optical component can be coupled to a control unit that generates a manipulator signal, wherein the manipulator signal initiates a change in the individual optical effects of the manipulated optic. Manipulator signals can be generated in different ways. In some embodiments, a metrology system is provided that allows for the measurement of the surface topography of the substrate surface in the measurement zone containing the exposure zone. Alternatively, the substrate surface data can also be derived from the data contained in the lookup table, which represents the measured or calculated topography of the substrate in the region containing the exposed regions.

When the system is configured to allow for distortion of other aberrations caused by the non-ideal surface shape of the reticle, corresponding means can be implemented to cope with the uneven surface shape of the reticle. Corresponding reticle surface data representative of the reticle surface contour in the reticle region corresponding to the exposure zone can be generated, for example, based on measurements or based on data contained in the lookup table. The reticle surface data can be processed by the control unit to generate a manipulator control signal, and then used to control at least one of the manipulation devices within the projection objective, and dynamically adaptively project the imaging properties of the objective lens in a compensated manner to reduce the area of the reticle The imaging aberration caused by the surface contour.

Figure 10 shows a second embodiment of a catadioptric projection objective 1000 of an immersion lithography at about λ = 193 nm according to different designs. In the case of a reduced imaging scale of 4:1 (β=-0.25), the projection objective is telecentric on the object side, and the image side numerical aperture NA=1.32 on the image side. The effective image field size is 26 mm x 5.5 mm. This specification is shown in Tables 10 and 10A. Figure 10A shows a section in the x-z plane, while Figure 10B shows an individual section in the y-z plane perpendicular thereto. The specifications for the system are derived from the embodiment shown in Figure 7 of US 2008/0174858 A1. This corresponding disclosure is hereby incorporated by reference.

The projection objective 1000 is designed to project a pattern image on a reticle of a flat object surface OS (object plane) onto a flat image surface IS (image plane) at a reduced scale, for example 4:1, wherein exactly two actual images are produced. Intermediate images IMI1, IMI2. The rectangular effective object field OF and the image field IF are off-axis, that is, the whole is outside the optical axis OA. The first refractive objective portion OP1 is designed to image the pattern of the surface of the object as the first intermediate image IMI1. The second reflection-refractive (refractive/reflecting) objective portion OP2 images the first intermediate image IMI1 as a second intermediate image IMI2 at a magnification close to 1: (-1). The third refractive objective portion OP3 images the second intermediate image IMI2 to the image surface IS with a strong reduction ratio.

The projection objective 1000 is an example of a "chain" projection objective having a plurality of series of objective portions, each serving as an imaging system, and an image generated by a previous imaging system on the radiation path via an intermediate image link (intermediate image) As an object of the subsequent imaging system on the radiation path. The order is refractive-refractive-refractive (RCR).

The chief ray CR path of the outer field point of the off-axis object field OF is shown in the bold line of Figure 10B to help follow the beam path of the projected beam.

Three mutually conjugated tantalum surfaces P1, P2, and P3 are formed at positions where the chief ray intersects the optical axis. The first pupil surface P1 is formed on the first objective portion between the surface of the object and the first intermediate image, and the second pupil surface P2 is formed on the second objective portion between the first intermediate image and the second intermediate image, and the third aperture The surface P3 is formed in a third objective portion between the second intermediate image and the image surface IS.

The second objective lens portion OP2 includes a single concave mirror CM that is tied to the second meandering surface P2. The first planar folding mirror FM1 is arranged to optically approach the first intermediate image IMI1 at an angle of 45° of the optical axis OA, and to reflect radiation from the surface of the object in the direction of the concave mirror CM. The second planar folding mirror FM2 has a plane mirror surface that is aligned at right angles to the plane of the first folding mirror, and reflects radiation from the concave mirror CM to a direction parallel to the image surface of the object surface. The folding mirrors FM1, FM2 are in the vicinity of the closest intermediate image, but at a small distance from them. Therefore, the folding mirror is a field mirror. Therefore, the double pass region in which the radiation passes twice in the opposite direction is geometrically formed between the deflecting mirrors FM1, FM2 and the concave mirror CM. A negative group NG having two negative lenses is placed close to the concave mirror having a large edge ray height and coaxial with the concave mirror, with the radiation passing through the negative group twice in the opposite direction. No optical elements are placed between the negative group and the concave mirror.

The first optical element next to the object surface OS is a transparent planar parallel plate PP, placed very close to the object field. Table B below provides information on the edge ray height MRH, the chief ray height CRH, the ray height ratio RHR, and the subaperture ratio SAR of the entrance face 1 and the exit face 2 of the plate PP:

This plate is associated with the manipulator MAN, allowing the two-dimensional distribution of the refractive index of the plate to be varied with high spatial resolution in response to electrical signals on short time scales. The architecture of the manipulator can be based on the wiring grid manipulator system disclosed in WO 2008/034636 A2, which is incorporated herein by reference. A cooling system for actively cooling the transparent manipulator elements can be provided to increase dynamics and allow for rapid temperature changes.

Furthermore, manipulation can be performed by relative displacement of aspheric surfaces having complementary shapes, as shown in EP 0 851 304 B1. A pair of aspheric surfaces can be placed adjacent to the surface of the object as a field element. An optoelectronic controller can also be used. Furthermore, the manipulator can be configured to include cylindrical lens elements that are rotatable relative to one another (see, for example, EP 0 660 169 B1) and placed near a field surface, such as an object surface.

As in the first embodiment, three correction scenarios SC1, SC2, and SC3 are simulated for compensation. In the first scenario SC1, the substrate irregularity is corrected in a conventional manner by actively manipulating the z-position of the wafer and the tilt state of the wafer, substantially as illustrated in FIG. In the second context SC2, an active manipulation of the plurality of optical elements is additionally performed, as described above.

In the third scenario SC3, the temporally dependent transverse index inhomogeneities applied within the planar panel PP during the scanning operation are used to dynamically optimize the field curvature and other field aberrations of the projection objective. The two-dimensional (space) distribution of the refractive index can be described by, for example, the Rennick coefficients Z2 to Z49.

Figure 11 shows a comparison of aberrations caused by quadratic irregularities (PV = 45 nm) in the three contexts SC1, SC2, and SC3. The overall induced aberration is decomposed into contributions as described by the Rennick coefficient, which is shown in the abscissa value of FIG. The ordinate shows the scanning aberration in nm. In the case where the plate-like optical element PP is dynamically actuated during the scanning operation to improve aberrations, it can be seen that the scanning aberration is significantly improved. Both the out-of-focus aberration (Z4) and the wavefront tilt aberration (Z2/3) can be significantly reduced with respect to the standard situation SC2, and are more reduced with respect to the first situation SC1, which is only relative to the axial position and tilt Use optimized wafer locations. Both out-of-focus (Z4) and wavefront tilt (Z2/3) are about 90% lower than the standard scenario SC2, and even better than the pure wafer scenario SC1 by about 93%. For example, by dynamically modifying the refractive index profile of the plate PP, the out-of-focus aberration Z4 can be reduced from about 12 nm to about 0.8 nm. Similarly, a significant improvement can be obtained for astigmatism (Z5/6), which can be reduced by about 90% relative to standard context SC2. The parasitic astigmatism aberration Z2/3 is reduced from 0.7 nm (in the second scenario SC2) to 0.3 nm in the third scenario SC3.

These values indicate that the dynamic modification of the refractive power distribution in the field plate PP significantly reduces the contribution of substrate surface irregularities to the focus budget, which is one of the current leading contributions. This results in a significant improvement in program latitude in the lithography program. At the same time, the requirements for focus errors can be relaxed on other contributing effects, such as lens heating or the like.

The embodiment shows that in the case where the surface of the substrate to be exposed is not perfectly flat in the exposed area, the dynamic change of the imaging properties (e.g., the field curvature of the projection objective) during the scanning operation can significantly improve the degree of aberration of the entire exposure process. however. This is one of many problems that can be solved or caused by providing a projection exposure system with a steering device that allows for objective changes in the imaging properties of the projection objective during a single scanning operation. Another problem that can be solved by this improved structure and function is the problem known as "mask bending".

In general, in a typical exposure system, the projection objective is aligned with the optical axis in the direction of gravity. The patterned mask is typically oriented at a horizontal plane and perpendicular to the optical axis. Thus, the reticle (mask) may sag due to gravity, which is essentially a function of the type of reticle and the mounting technique that secures the reticle to the reticle holder. In general, the two-dimensional deviation occurring from the plane alignment of the pattern may not be known in advance and may be difficult to determine. The result of the sag causes the individual positions on the reticle to be imaged to be offset from the desired position (in the case of a perfect planar reticle) and cannot be completely predicted in advance, the direction and length of this displacement being usually the position on the reticle. function. Another possible factor contributing to the sag of the reticle is the direct influence of the mounting technique on the shape of the reticle. In general. The forces and moments caused by the bearings and/or holdings acting on the reticle may contribute to the complex deformation state of the reticle during exposure. These effects may not be fully known in advance and may vary from mask to mask, but may be the same for the mask category.

The problems caused by the bending of the reticle are often solved in various ways, for example the examples disclosed by the applicant in WO 2006/01300 A2 or US 2003/0133087 A1.

The aberration problem caused by the reticle bend can be utilized in a dynamic manner for exposure devices used to dynamically change the imaging properties of the projection objective during scanning operations.

Figure 12 shows in a perspective view the deformation of the surface of the curved reticle in terms of quality. If the reticle is fixed to the frame by the support, it can be assumed that the deformation is substantially parabolic in shape as shown in WO 2006/013100 A2. If the reticle is assembled by the clamping technique at three or more points in the peripheral region of the reticle, saddle deformation may occur, which is superimposed on the deformation caused by gravity. Such a saddle deformation is shown in Figure 12, in which the reticle is held in four corner positions. Curving of the reticle may cause the central region of the reticle to be displaced by a factor of one tenth or more of the micrometer relative to the edge region. During the adjustment of the projection objective, the bending effect of the systematic reticle can be coped with by means of offsetting, so that the projection objective has a defined non-zero field region which copes with a certain amount of reticle bending. however. The unsystematic contribution caused by the unpredictable temperature caused by the different reticle and/or deformation during operation may not be dealt with in advance by the corresponding adjustment of the projection objective. Unpredictable effects may have a significant contribution to the focused budget and may not be able to fully cope with the corresponding aberration effects using standard controls. However, actively manipulating at least one field element in a dynamic manner during a scanning operation can significantly improve the degree of aberration toward smaller values.

Figure 13 shows a comparison of two corrected scenarios. The figure shows the residual aberration after the manipulator is adjusted. The column shows the residual error (scanning aberration) of the reticle (saddle) deformation of the reticle with 40 nm PV distortion at the center of the reticle. In comparison, the solid line SC3 is shown in Fig. 7 as an individual value in the correction context of the target modified embodiment of the two concave mirrors CM1, CM2 (field mirror). In the uncorrected system, the out-of-focus value Z4 is about 7 nm. In standard scenario SC2, the out-of-focus error can be reduced to approximately 3.5 nm. The additional target deformation of the reflecting surfaces of the mirrors CM1, CM2 can further reduce the level of defocusing by about 0.3 nm. At the same time, the parasitic error caused by this correction is usually small, about 0.5 nm as shown.

A similar study has been performed for a second embodiment using a transparent field PP element coupled to a manipulator to allow for a two-dimensional distribution of refractive indices within the panel. Figure 14 shows a comparison of three correction scenarios. The standard correction allows the focus error (Z4) to be reduced from 7 nm to about 6 nm. The use of a two-dimensional manipulator acting on the field elements near the surface of the object allows for a significant reduction in these errors. In particular, the out-of-focus aberration can be reduced from about 6 nm to about 0.4 nm without introducing parasitic field aberrations above a critical level. Furthermore, with a two-dimensional manipulator placed close to the surface of the object, the tilt error Z2/3 can be reduced from about 16.8 nm to about 0.6 nm in context SC1 (wafer handling only).

Figure 15 shows another alternative example of manipulating the optical properties of a projection objective by bending one or more reflective surfaces of the mirror disposed optically near the field surface during scanning. Figure 15 shows details of the meridian plane of the projection objective, with all of the optical components having the same specifications as described in Figures 10A, 10B. Therefore, the specifications of the optical system partially shown in Fig. 15 are the same as those provided in Tables 10 and 10A. As described above, the second objective lens portion OP2 includes a concave mirror CM positioned adjacent to the second pupil surface P2 of the projection objective lens, the optical position of which is in the first intermediate image IMI1 (generated by the first objective lens portion) and the second intermediate image IMI2. (which is ultimately imaged by the third refractive mirror portion to form an image on the image surface). The first folding mirror FM1 is disposed to be optically close to the first intermediate image, and reflects the radiation provided by the first objective portion OP1 toward the concave mirror CM. The second folding mirror FM2 is disposed at 90° with respect to the first folding mirror FM1, and is disposed to be optically close to the second intermediate image IMI2, and reflects radiation from the concave mirror CM toward the image surface. The reflective faces of both the first folding mirror and the second folding mirror are substantially flat (planar) in the nominal operating state, wherein the nominal state is not optically capable and the only function is to deflect the incident radiation. Table C below provides information on the edge ray height MRH, the chief ray height CRH, the ray height ratio RHR, and the subaperture ratio SAR of the first folding mirror FM1 and the second folding mirror FM2. In particular, it is easy to know from the subaperture ratio that both folding mirrors are located very close to the field surface (SAR is close to zero).

In this embodiment, the portion of the folding mirror carrying the mirror coating has a limited range of elasticity, so that the reflecting surface area can be bent to some extent in response to an external force. Some actuators of the first mirror manipulator MM1 associated with the first folding mirror FM1 (indicated by arrows) and some actuators of the second mirror manipulator MM2 associated with the second folding mirror FM2 (indicated by arrows), Operatively coupled to the back side of the resilient portion of the individual mirror. The actuator is controlled by a mirror control unit MCU, which can be an integral part of the central control unit of the projection exposure apparatus. The manipulator control unit is coupled to receive signals indicative of the desired deformation of the individual mirror surfaces or without deformation. Each mirror manipulator is used to bend the associated reflective surface in only one dimension (eg, the cylindrical shape of the mirror surface) or in two dimensions (eg, a substantially concave or convex spherical or aspherical mirror surface shape).

The bending manipulation of the one or two folding mirrors in the inward and/or outward direction allows for a greater degree of freedom, in particular the optical performance of the projection objective relative to the field aberrations. During the scanning operation, the mirror surface can be deformed in a time dependent manner to reduce unwanted aberrations, such as aberrations due to unevenness of the substrate surface. Since there are two manipulators that can operate independently of each other, different aberrations can be corrected independently of each other. Furthermore, in the case where a single mirror manipulation is not sufficient to provide a range of manipulation to compensate for some aberrations, an additional range of manipulation is available. The effect that can be obtained by manipulating the folding mirror can be similar to that obtained by manipulating a concave mirror disposed close to the intermediate image as described in FIGS. 7A and 7B. Therefore, you can refer to the relevant instructions. In addition to other manipulators, such as the transparent manipulator MAN formed by the planar panel PP of Figure 10B, one or more folding mirrors with active deformable reflective surfaces can be provided to provide further freedom. Other embodiments do not have a flat panel and can be manipulated in the manner described.

It has been shown by various embodiments that correcting field aberrations, such as field curvature, during scanning operations of a scanning projection exposure apparatus can significantly reduce imaging aberrations due to deviations of the substrate surface and/or pattern surface from the ideal planar shape. . In particular, the negative effects of wafer unevenness and/or reticle bending in a scanning exposure system can be significantly reduced.

The description of the above preferred embodiment is used as an example. It will be apparent to those skilled in the art that the invention may be Therefore, it is intended to cover all such changes and modifications within the spirit and scope of the invention, as defined by the scope of the claims.

The contents of all patent applications are incorporated herein by reference.

700. . . Projection objective

1000. . . Projection objective

CM, CM1, CM2. . . concave mirror

DOF. . . Depth of focus

EA. . . Exposure area

EAX. . . width

EAY. . . length

ES. . . Exit surface

FM1. . . Folding mirror

FM2. . . Second folding mirror

FOC. . . Focus position

IF. . . Irradiation field

IF _D . . . Design image field

ILL. . . Irradiation system

IM. . . Infiltration medium

IMI1. . . First intermediate image

IMI2. . . Second intermediate image

IS. . . Image surface

M. . . Mask

MCU. . . Mirror control unit

MM1. . . First mirror manipulator

MM2. . . Second mirror manipulator

NA. . . Numerical aperture

NG. . . Negative group

OA. . . Optical axis

OF. . . Off-axis object field

OP1. . . First objective part

OP2. . . Second objective part

OP3. . . Third objective part

OS. . . Object surface

P1, P2, P3. . .瞳 surface

PCL. . . Plano-convex lens

PO. . . Projection objective

PS. . . Petzval surface

PV. . . Peak-valley

RD. . . Receiving device

RS. . . Device

S. . . Substrate

SCA. . . Scanning aberration

SS. . . surface

W. . . Wafer

WS. . . Wafer scanner

Figure 1 shows a schematic view of an embodiment of a projection exposure apparatus for lithography having an illumination system and a projection objective;

Figure 2 shows a schematic diagram of the effects of different field curvatures on the imaging procedure;

Figure 3 shows a schematic diagram of a conventional principle for correcting out-of-focus errors using a wafer platform that can rise or fall parallel to the optical axis;

4A shows a semiconductor wafer having a plurality of exposed regions (die), a selected rectangular exposure region is shown in FIG. 4B, and a vertical cross-sectional view of the exposed region of the uneven substrate surface is shown in FIG. 4C;

Figure 5 shows the Nickel spectrum showing the effect of the selected aberration on the substantially quadratic surface profile in the x-direction in the exposure zone;

Figure 6A shows the scan field profile at the different exposure time in the exposure zone, and Figure 6B shows the individual curvature of the image field of the dynamically manipulated projection objective to conform to the surface shape of the exposure zone within the individual image field position;

Figure 7 shows two axial portions of a first embodiment of a catadioptric projection objective comprising two concave mirrors optically adjacent to the intermediate image and associated with the dynamic mirror manipulator;

Figure 8 shows a schematic diagram of the aberrations caused by the uneven substrate surface and decomposed into the contributions described by the Rennick coefficient for three different compensation modes;

Figure 9 is a view schematically showing the surface deformation of the two concave mirrors of Figure 7, partially compensating for the aberration caused by the uneven surface profile of the substrate;

Figure 10 shows a portion of a second embodiment of a catadioptric projection objective comprising a transparent manipulator element in close proximity to the surface of the objective;

Figure 11 shows a schematic diagram of aberrations resulting from the uneven substrate surface and decomposed into contributions described by the Rennick coefficient for three different compensation modes;

Figure 12 is a three-dimensional view showing the saddle deformation of the reticle;

Figure 13 is a schematic illustration of aberrations resulting from the uneven mask surface and decomposed into two different compensation modes for the contribution described by the Rennick coefficient in an embodiment having two deformable field mirrors;

Figure 14 is a schematic diagram showing three comparisons of bending modes for skewed reticle in an implementation having transparent manipulator elements near the surface of the object;

Figure 15 shows an embodiment detail of two folding mirrors that can be deformed independently of each other by a mirror manipulator.

EA. . . Exposure area

EAX. . . width

EAY. . . length

PV. . . Peak-valley

SS. . . surface

W. . . Wafer

Claims (21)

A projection exposure method, comprising: exposing an exposure area of a radiation sensitive substrate disposed on an image surface of an object of the projection objective by using a pattern of a reticle disposed on a surface of the object of the projection objective in a scanning operation, The scanning operation includes moving the reticle in a first scanning direction relative to the effective object field of the projection objective and simultaneously moving the radiation sensitive substrate in a second scanning direction with respect to an effective image field of the projection objective; and During the scanning operation, the imaging properties of the projection objective are actively changed according to a schedule to dynamically change at least one aberration of the projection objective during the scanning operation, wherein: (i) actively changing at least the projection objective An aberration step includes dynamically changing a field curvature of the projection objective according to the schedule during the scanning operation; (ii) the projection objective comprises a first field element comprising a mirror having a reflective surface, Arranging at a position of a projection beam path of the projection objective that is optically close to a surface of the projection objective; and (iii) changing the projection The curvature of the field of the objective lens includes adjusting a surface profile of the reflective surface of the mirror, from a single radius of curvature having a first value to an optically used region before adjustment to a second value after adjustment in the region of the optical use. a single radius of curvature to change a spatial school of the spatially resolved manner of the mirror; wherein the adjustment results in an adjusted single radius of curvature, and the second value is different from the first value. The projection exposure method of claim 1, wherein the projection objective comprises a second field element, and wherein the method comprises manipulating the first and second field elements independently of each other. The projection exposure method of claim 1, wherein the curvature of the field is changed by a rate of change between 0.5% and 50% of the focal depth of the projection objective over a time interval of 1 ms. The projection exposure method of claim 1, wherein the direction change of at least one aberration is changed one or more times during a single scanning operation. The projection exposure method of claim 1, wherein the imaging property is changed at a frequency of at least 20 Hz. The projection exposure method of claim 1, further comprising the steps of: generating a data indicating a surface profile of the radiation-sensitive substrate in the exposure region of the radiation-sensitive substrate; generating a manipulator control based on the data a signal; the at least one manipulation device of the projection objective is driven by the controller control signal to dynamically adapt the imaging property of the projection objective to reduce imaging aberration caused by the surface contour of the exposure region of the radiation sensitive substrate . The projection exposure method of claim 1, further comprising the steps of: generating a data indicating a surface contour of the exposed area of the reticle; generating a manipulator control signal based on the data; Controlling a signal to drive at least one manipulation device of the projection objective to dynamically adapt the imaging property of the projection objective while reducing the reticle The surface profile of the exposed area causes imaging aberrations. The projection exposure method of claim 1, wherein the first field element is a transparent optical element on the projection beam path, and a spatial distribution of refractive power is changed in an optically used area of the transparent optical element. A two-dimensional refractive index distribution of the transparent material of the transparent optical element is obtained by locally heating the transparent material of the transparent optical element by a target. The projection exposure method of claim 8, wherein the first field element is a plane mirror, and a spatial distribution in which a refractive power is changed in an optically-used region of the transparent optical element comprises disposing the transparent optical element, It is parallel to one of the optical axes of the projection objective. A projection exposure apparatus comprising: an illumination system for generating illumination radiation irradiated on a mask having a pattern; a projection objective for projecting the pattern onto a radiation sensitive substrate; and a scanning system for During the scanning operation, the illuminant is moved in a first scanning direction with respect to the effective object field of the projection objective, and the radiation sensitive substrate is moved in a second scanning scanning direction with respect to an effective image field of the projection objective. And a control system for actively changing the imaging properties of the projection objective according to a schedule during the scanning operation to dynamically change at least one aberration of the projection objective during the scanning operation, wherein: i) the projection objective comprises a first field element comprising a mirror having a reflecting surface disposed at a position of a projection beam path of the projection objective, Positioned optically adjacent to a field surface of the projection objective; (ii) the projection objective includes a first field element for changing a surface profile of the reflective surface of the mirror in an optically used region; (iii) actively changing The step of projecting at least one aberration of the objective lens includes dynamically changing a field curvature of the projection objective according to the schedule during the scanning operation; (iv) changing the curvature of the field of the projection objective comprises adjusting the reflection of the mirror a surface profile of the face, from a single radius of curvature having a first value to an area used for optics to a single radius of curvature adjusted to have a second value in the area used for the optics; and (v) the adjustment results in The adjusted single radius of curvature, and the second value is different from the first value. A projection exposure apparatus according to claim 10, wherein the first means is adapted to change the shape of the reflecting surface of the mirror in two dimensions. The projection exposure apparatus of claim 10, wherein the projection objective comprises a second field element, each of the first and second field elements is associated with a manipulation device, and the manipulation device is independent of each other in a predetermined coordinate manner. Ground control. The projection exposure apparatus of claim 10, wherein the control system is configured to change the curvature of the field by a rate of change between 0.5% and 50% of the focal depth of the projection objective over a time interval of 1 ms. . The projection exposure apparatus of claim 10, wherein the control system is configured to change a change in direction of at least one aberration during a single scanning operation One or more times. The projection exposure apparatus of claim 10, wherein the first field element is a transparent optical element on the projection beam path, and the spatial distribution of the refractive power is changed in an optically used area of the transparent optical element. A two-dimensional refractive index distribution of the transparent material of the transparent optical element is obtained by locally heating the transparent material of the transparent optical element. The projection exposure apparatus of claim 15, wherein the first field element is a plane mirror, and a spatial distribution in which a refractive power is changed in an optically-used region of the transparent optical element comprises disposing the transparent optical element, Parallel to one of the optical axes of the projection objective. The projection exposure apparatus of claim 10, wherein the projection objective comprises: a first objective portion, the pattern provided on the surface of the object is imaged as a first intermediate image; and a second objective portion is to be The first intermediate image is imaged as a second intermediate image, the second objective portion includes a single concave mirror on a second surface; a third objective portion images the second intermediate image onto the image surface; a mirror disposed optically adjacent to the first intermediate image such that the first folding mirror reflects radiation from the surface of the object to a direction of the concave mirror; and a second folding mirror disposed optically adjacent to the second intermediate image And causing the second folding mirror to reflect radiation from the concave mirror to a direction of the image surface, wherein the manipulation device is configured to at least the first folding mirror and the second folding mirror One of the optical zones used to change the surface profile of the reflective surface. The projection exposure apparatus of claim 17, wherein each of the folding mirrors is associated with a manipulation device, and the manipulation devices are adapted to change the surface contour of the folding mirror independently of each other in a predetermined coordinate manner. A projection exposure method, comprising: exposing an exposure area of a radiation sensitive substrate disposed on an image surface of an object of the projection objective by using a pattern of a reticle disposed on a surface of the object of the projection objective in a scanning operation, The scanning operation includes moving the reticle in a first scanning direction relative to the effective object field of the projection objective while moving the radiation sensitive substrate in a second scanning direction with respect to an effective image field of the projection objective; During the aiming operation, the imaging properties of the projection objective are actively changed according to a schedule to dynamically change at least one aberration of the projection objective during the scanning operation, wherein the direction of at least one aberration changes during a single scanning operation The system changes one or more times; and wherein the adjustment results in an adjusted single radius of curvature, and the second value is different from the first value. The projection exposure method of claim 19, wherein the imaging property is changed at a frequency of at least 20 Hz. The projection exposure method of claim 19, wherein a field curvature of the projection objective is dynamically changed according to the schedule during the scanning operation.